Photopheresis is a treatment involving the separation of white cells from the blood, addition of a photoactivatable drug, and U.V. irradiation of the white cells before reinfusion to the patient. In known photopheresis systems, the blood is pumped by peristaltic roller pumps. Such roller pumps require use of complex tubing sets and have the potential to cause cell damage under high outlet pressure conditions. Alternatively, blood has also been pumped with discrete pump chambers and valves which also require complex tubing sets. Such discrete pump chambers and valves are considered to be less damaging to cells under high outlet pressures.
A very real advancement in photopheresis systems would result if the size and complexity of the associated tubing could be reduced, even at the cost of a more complex driving system, since the driving system is permanent equipment and the tubing set must be replaced after each treatment session. Such a result has been accomplished with peritoneal dialysis systems, where the flow of dialysate is controlled entirely with diaphragm pumps and valves driven by air pulses delivered to a molded cassette through a plastic membrane. The cassette contains all components of a previously complex tubing set, except for the lines to the patient and short delivery lines from the dialysate containers. The air pulses are controlled by continually analyzing the pressure changes in the air delivered to the diaphragm, processing them through a computer, and making continual corrections as a result. This resulting system is able to accurately measure the fluid delivered, but is unable to provide a fixed steadiness of flow rate. In contrast to peritoneal dialysis systems, systems such as photopheresis systems, which involve continuous blood cell separation, require both a very steady flow rate, as well as the ability to control the fluid flow rate.
It is therefore an object of the present invention to provide a pump that achieves an accurate, steady flow rate, and which may be used to facilitate blood cell separation during photopheresis treatment of diseases.
These and other objects and advantages of the invention will become more fully apparent from the description and claims which follow or may be learned by the practice of the invention.